PV solar panel switch

Discussion in 'Analog & Mixed-Signal Design' started by jmmediavilla, Dec 18, 2017.

  1. jmmediavilla

    Thread Starter New Member

    Jan 24, 2014
    4
    0
    Hello, my name is Javier Martin (from Spain) and this is my first post (pls., forgive my English).


    I am bulding a solar air can panel for heating air (there is plenty of information on the internet for this device so I will not go in details about it).


    There is a fan (20 W, 12 Vcc) and a PV solar panel to run the fan. The idea is very simple: when the sunlight increase, the heating of the solar air can panel increases and the output of the PV solar panel increases and the speed of the fan increases also.

    It is very simple and woks fine but the problem is when the output of the PV solar panel is too low (below 5 Vcc), the fan does not work properly.


    So, is there a simple way to compare the output of the PV solar panel and if it is, lets say, below 5 Vcc then the voltage to the fan would be 0 Vcc. If the output of the PV solar panel is bigger than 5 Vcc then the voltage of the fan woul be the voltage of the PV solar panel?


    Thanks and best regards,


    Javier Martin
     
  2. Kjeldgaard

    Member

    Apr 7, 2016
    373
    129
    If the fan is connected directly to the solar panel, then it may be the startup current that is the problem?

    I would try with an electrolytic capacitor of at least 1000μF and at least 25 volts as a starter buffer in parallel with the solar cell and fan (remember polarity for all three components).
     
  3. jmmediavilla

    Thread Starter New Member

    Jan 24, 2014
    4
    0
    Hello, the problem is on sunrise or sunset that the voltage of the solar cell is quite low (also when it is very cloudy). In this case (less than 5 Vcc) the fan behavior is not good: the noises it makes, sometimes it run a little bit then stops, so I want to avoid the fan running in this gap (between 0 to 5 Vcc, +/-).
    Thanks,
    Javier Martin
     
  4. Kjeldgaard

    Member

    Apr 7, 2016
    373
    129
    Have you tried any capacitor to start assistance to the fan?

    Especially with low solar radiation, the output voltage from solar cells is very soft and a fan typically needs a larger start current.
     
  5. Picbuster

    Well-Known Member

    Dec 2, 2013
    978
    126
    Hi,
    If I understand you well than a voltage cut down system is what you need.
    If solar output voltage = above wanted voltage fan is connected else do not connect.
    You do need hysteresis to avoiding intermitted switching problems. ( eq on at 5.5V and of at 4.5V)
    If this is correct than you can use a pic12f675 running from a 2.5 supply and a Fet to control the fan.
    The 2.5V from solar very simple program to control fan and hysteresis.
    using a fet and zener is the other way but will grant no stable system.

    Picbuster
     
  6. jmmediavilla

    Thread Starter New Member

    Jan 24, 2014
    4
    0
    Hi, thanks for your answers.
    I will try a capacitor to start assistance to the fan and let you know how it works.
    Picbuster, that is right I need a voltage cut down system, also with the hysteresis. What is a pic 12f675?
    Thanks,
    Javier Martin
     
  7. Bernard

    Expert

    Aug 7, 2008
    5,225
    600
    Solar Gleaner # 2 00000.png Here is an old circuit that illustrates what I think you want. The fans tested started with out
    help but produced little output, but with circuit and large cap. could give useful bursts-- I have to go-
     
    jmmediavilla likes this.
  8. jmmediavilla

    Thread Starter New Member

    Jan 24, 2014
    4
    0
    Hello, I have made some test with and without the electrolytic capacitor.

    It is not 100% real because I move the solar cell to simulate the moving of the sun but it give us an idea of the performance of the fan. Here is the data:

    Without the capacitor: the fan is running. I move the solar cell to decrease the output. Until 3.5 V (250 mA) the fan is running well. At 3.08 V (80 mA) the fan stops. Now I move the solar cell to increase the output. At 3.2 V (200 mA) the fan start running.

    With the capacitor (2200 uF/25 V): the fan is running. I move the solar cell to decrease the output. At 3.09 V (80 mA) the fan stops. Now I move the solar cell to increase the output. At 3.17 V (200 mA) the fan start running.

    So there is not big difference.

    In the real, at the sunrise and sunset, the fan would be some time with a consumption up to 200 mA without running. I think it would not do any good to it so I will try to avoid it.

    I will try the voltage comparator with the LM393N to start running at about 4 Vcc and stop at about 3.5 Vcc (or similar).

    For now I will not try the idea of the pic12f675 but I will keep it in mind just in case.

    I will let you know how it goes.

    Thanks and best regards,

    Javier Martin
     
Loading...